Large distributed user data services may serve millions of clients. For example, email services, calendar services, and other types of user data services may store user-specific data for each of millions of users or clients on one or more distributed data servers. Each different user or client may engage in varying degrees of activity, and may access the system via various types of interfaces. Further, the size of each client's data may vary from one client to the next. For example, a first user may store several gigabytes of email data via an email server, while a second user may store only a few kilobytes or megabytes of email data via the same email server. As another example, several different users may store varying amounts of data such as personal photo files via the same server, or the different users may store varying amounts of data such as calendar information via the same server. The number of such users or clients may range from hundreds to thousands, millions, or billions of users. Additionally, the users or clients may dynamically store or delete their own user data, or may send messages to others, or may receive messages from others, resulting in more dynamic activity.
Placement of a user's individualized data, including backup copies of the individualized data, may have an impact on system performance, for example, in terms of latency of serving data to users, efficiency of service network utilization, and redundancy of the system in terms of resilience to failures. As another example, a user may be associated with a particular geographic region, in terms of network connection, with which the client may be physically located most of the time. For example, the client may be associated with Europe, the eastern coast of the United States, etc. For example, if the client is physically located in Peoria, Ill. (i.e., in the midwestern part of the United States), then the system may suffer network latency issues if the client's data is physically stored on one or more servers in Australia or India.
In addition, users may have a provider agreement or contract such as a service level agreement that may include provisions for preferred (e.g., gold) clients or that may include legal provisions such as “data must be kept in United States.” For example, a European client may prefer a service agreement providing that the client's “data must be kept out of the United States” in order to avoid potential issues involving the Patriot Act.